Hydraulic fluid



parted Dec. 15, 1942 HYDRAULIC FLUID John G. Woodhousc, Cragmere, and Kenneth E. Walker, Elmhnrst, Del., assignors to E. L du Pont de Nemonrs & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application May 14, 1940, Serial No. 335,140

. 11 Claims. (Cl. 252-73) of this fluid or to provide greater fluidity where This invention relates to compositions of matter and more particularly to fluids for use in hydraulically operated apparatus such, for example, as hydraulic brakes, hydraulic clutches, and similar hydraulically operated mechanisms.

Various proposals have previously been made involving the use of mixtures of alcohol and castor oil, glycerine and the like, for transmission of power such as in actuating pressureoperated elements of hydraulic brake systems, shock absorbers, hydraulic clutches and similarly operated apparatus. In a great number of such previously proposed fluids, however, there have been practical disadvantages such, for example, as wide changes in viscosity, corrosive or degrading eil'ects of the fluids upon rubber and metal parts of hydraulic apparatus, tendencies toward gasification and solidification under higher and lower temperature conditions, respectively; all of these and similar disadvantages being drawbacks to successful commercial utilization of previously proposed fluids.

It is an object of the present invention to overcome these and other undesirable characteristics and disadvantages and particularly to produce an improved hydraulic fluid characterized by general utility under extremely variable operating conditions.

Other objects and advantages of this invention will be apparent by reference to the following specification in which its preferred details and embodiments are described.

According to this invention improved hydraulic fluids are prepared by utilizing as an ingredient the cyclic acetal, containing a free-hydroxyl group, of ethylene glycol and hydroxy acetaldehyde, namely, 2-hydroxy methyl-1,3-dioxolane. This material is a colorless liquid having a boiling point of about 96 C. at 30 mm. and is represented by the formula:

OCH:

HOOHzCH cies underthe temperature conditions normally encountered in automobile operation.

We have found that the amount of Z-hydroxy methyl-1,3-dioxolane may fall generally within the range of 5 to 95%, it sometimes being desirable to augment the lubricating characteristics extremes of temperature are encountered by adding to the fluid of this invention one or more lubricants, solvents, or diluents. Thus, as a lubricant, there may be used any oil, soluble in the solvent or mixtures of solvents employed, whether mineral, vegetable or animal but the term animal oil is used hereinafter in the broad sense to include all terrestrial animal, marine animal and flsh oils. Preferably, we utilize an oil characterized by being a glyceride or other ester of fatty acids, and morespecifically, one which contains hydroxy or unsaturated groups, or both. Thus, for example, among the many oils which we may utilize according to this invention there may be mentioned almond, blackflsh, candlenut, castor, China-wood, coconut, cod, corn, cottonseed, croton, eucalyptus, geranium, grape seed, hemp, junipe lard, lemon, linseed, mustard seed, menhaden, neats foot, olive, oiticica, orange, palm,

peanut perilla, porpoise, rapeseed, seal, sesame,

sharp sperm, tallow, train, soyabean, sunflower,

' teaseed, tung, walnut, whale, wool and the like.

Blown oils such as blown castor oil, blown corn oil, blown cottonseed oil; blown peanut oil, and blown soyabean oil maybe utilized alone or in combination with other oils and oil derivatives or both.

Derivatives of these oils may also be utilized as the lubricant portion of the. hydraulic fluid, such as, for example, those derivatives which may be obtained by alcoholysis of these vegetable or animal oil esters or the blown oil esters with a compound containing one or more hydroxyl groups capable of such alcoholysis reaction. Suitable compounds containing one or more hydroxyl groups are: 2-hydroxymethyl1,3-dioxolane or any simple alcohol or alcohol containing a functional group, such as amino, keto, aldo, ether, ethylenic or other unsaturated groups and the like. Thus, for example, desirable oil derivatives may be obtained by heating a vegetable or animal oil or blown vegetable or animal oil, as previously disclosed, with such monohydric alcohols as methyl, ethyl, normal and isopropyl, butyls, amyls, hexyls, heptyls, cetyls, nonyls, decyls, dodecyl, 2-ethy1 butyl and ethyl hexyl; the individual alcohol or mixture of branched chain alcohols obtainable by catalytic hydrogenation of oxide of carbon under pressure, such as 2-methyl butanol-1,3-methyl butanol-2, 2-methyl pentanol-3, 2-methyl pentanol-l, .2,4-dimethyl pentanol-3, 2,4-dimethyl pentanol-l, 2,4-dimethyl hexanol-3, 4-methyl hexanol-l, 2,4-dimethyl hexanol-l, 4-methyl heptanol-l, and the like.

Similarly, such dihydric alcohols and glycols may be used for alcoholysis of the oil as ethylene gly- 001, the 1,2- and 1,3-propylene glycols, the butylene and isobutylene glycols, the amylene and hexylene glycols, and the like, as well as polygiycols such as polyethylene glycol and di propylene glycol.

Trihydric alcohols such as methyl glycerin and other polyhydric alcohols may be utilized for alcoholysis of the oils disclosed previously, as well as the trihydric alcohols which contain functional groups in addition to hydroxyl groups. Further miscellaneous alcohols which may be utilized for alcoholysis with the animal or vegetable oils and which come within the scope of this invention include cyclohexanol, benzyl alcohol, naphthenyl alcohol, sorbitol, furfuryl alcohol and the like. Alcohols containing amino, keto, aldo, ether, ethylenic, or unsaturated groups which may be utilized are hydroxyethylamine, propionyl carbinol, glycolic aldehyde, glycol monomethyl ether, diethyl acetylene glycol monopropionate and alpha-gamma-butinenediol which are representative respectively of alcohols containing such functional groups. All of the specific mono-, diand trihydric alcohols hereinbefore set forth are representative and illustrative of ;the alcohols which may be utilized according to this invention for the production of derivatives of animal and vegetable oils, and should not be taken as a limitation thereof.

In the alcoholysis of vegetable or animal oils such as previously described, these mono-, di-, and trihydric alcohols, acetals or alcoholic bodies containing a hydroxyl group may be mixed with varying proportions of vegetable or animal oils, as previously described and heated preferably to a temperature of from 50-250 C. We may use stoichiometric proportions of oil and alcoholic bodies necessary for the alcoholysis reaction, but we prefer to use an excess of alcoholic body giving as high as 1 to 20 times the quantity required for complete reaction. This excess speeds up the reaction and enables its rapid completion under lower temperatures. The excess alcohol or alcoholic body may or may not be removed from the final product, as desired. We prefer to operate the process in the presence of catalysts such, for example, as potassium oleate or ricinoleate, potassium carbonate, potassium hydroxide, zinc oxide, lead oxide, and the like. We have found that catalyst concentrations of from about 0.01 to 8% (by weight, based upon the reaction mixture of oil plus alcoholic body) are satisfactory altho we prefer to utilize, about 0.5 to 6.5% concentration thereof. If desired, we may also operate the process in the presence of solvents, such as, ether, pyridine, and the like, which may, if desired, be thereafter utilized as ingredients of the final hydraulic fiuld composition. Pressures are utilized which are necessary to allow the use of temperatures which in turn will eifect a suitably rapid reaction rate, particularly where low boiling reactants are involved.

As a further feature of this invention we have found that the addition of small proportions of graphite, as such or in fiuid suspensions, such as those known under the trade-mark names Castor-dag," Aquadag," Glydag, or the like, is often beneficial and improves the characteristics of these fluids.

We may, for example, use Castordag (a suspension of graphite in castor oil) as the source of, all or part of the castor oil, and similarly Glydag" (a suspension of graphite in a polyalasoaaas cohol) as the source of part or all of the polyalcohol. We prefer to use graphite as such or in the form of suspensions such as previously disclosed so that the graphite concentration will be in a range of from about 0.001 to 0.5% by volume of the total fiuid.

Altho the Z-hydroxy methyl-1, 3-dioxolane of this invention is characterized by being relatively non-corrosive, if this ingredient or other ingredients with which it is mixed should react slightly with parts of the hydraulic system corrosion inhibitors may be used. Among the many .corrosion inhibitors which may be used are sodium nitrite, calcium nitrite, borax, sodium bichromate, potassium bichromate, sodium chromate, potassiumchromate triethanolamine oleate, triethanol amine ricinoleate, sodium phosphate, potassium phosphate, sodium acid phosphate, potassium acid phosphate and the like. The preferred amounts of inhibitor are from 0.1 to 2.0% although .05-to 3% will besatisfactory.

Although the 2-hydroxy methyl-1,3-dioxolane of this invention is admirably fitted by itself for hydraulic fluid purpose, it can be utilized in admixture or combination with one or more organic diluents. Among the organic material susceptible for admixture as diluents are: alcohols such as the monoand poly-hydrlc, alicyclic, aromatic and amine alcohols, including specifically methanol, propanol, butanol, isobutanol, octanol, dlacetone alcohol, ethylene and propylene glycol, glycerol, sorbitol, cyclohexanol, phenol, benzyl a1- cohol, triethanolamine and ethoxy amino butanol; organic esters such as ethyland butyl acetate; ethers such as diisobutyl, ethyl tertiary butyl, and methyl ricinoleyl ethers, methyl ether of ethylene glycol, ethyl ether of ethylene glycol and beta (methoxy methoxy) ethanol, butyl and isobutyl ether of ethylene glycol, ethyl ether of dlethylene glycol, and methyl ether of diethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, and diglycerinei aldehydes such as heptaldehyde and benzaldehyde; ketones such as diisopropyl ketone and cyclohexanone; nitrogen-containing compounds such as triethanolamine, dimethyl formamide, ethanol formamide, octyl amine; tetrahydrofurfuryl alcohol and furane compounds; hydrocarbons such as isooctane, benzene, and cyclohexane.

Solvents or diluents and oils above described may be used in ratios to the Z-hydroxy methyl- 1,3-dioxolane which vary over a wide range. Thus, with 5 to 95% by volume of the dioxolane, the diluents and lubricants may be employed in proportions of 5 to 95% by volume of diluent or lubricant, or, when employing mixtures of diluents and lubricants, 5 to 95% by volume of such a mixture may be used with 5 to 95% by volume of dioxolane, the mixture of diluent and lubricant varying from 1 to 99 parts of diluent to 99 to 1 parts of lubricant. Preferably, however, from 5 to 50% of a diluent or a lubricant or a mixture of the two is utilized with from 50 to 95% dioxolane.

The following specific compositions, as examples, will illustrate proportions of materials which may be utilized according to this invention.

Example 1.--l0 parts by volume of castor oil, parts by volume of 2-hydroxymethyl-l,3-dioxolane. The free acid of the oil may be neutralized with an alkali such as-potassium or sodium hydroxide.

Example 2.-10 parts by volume of castor oil (acid value of about 1), 20 parts by volume of 2- mixture. After reaction, 35 parts by volume 01' the reaction mixture were mixed with parts of 2-hydroxymethyl-1,3-dioxolane and parts of isobutanol to make a complete fluid.

Example 4.24.5 parts by volume of castor oil and 10.5 parts by volume of ethylene glycol were reacted for 30 minutes at 185 C. in the presence of 63 gms. of potassium soap per liter of reaction mixture. After reaction, to 35 parts of the above reaction mixture were added 35 parts of 2-hydroxymethyl-1,3-dioxolane and 30 parts of beta- (methoxy methoxy) ethanol to make a complete fluid.

Example 5.20 parts by volume of blown corn oil and 15 parts by volume of 2-hydroxymethyl- 1,3-dioxolane were reacted by heating for one hour at 180 C. in the presence of 47 gms. of potassium -soap per liter of reaction mixture. After reaction, to 35 parts of the reaction mixture, 25 parts of 2-hydroxymethyl-1,3-dioxolane and parts of methoxy ethanol were added to make a complete fluid.

Example 6.20 parts by volume of blown cottonseed oil and 15 parts by volume of ethylene glycol were reacted by heating for one hour at 180 C. in the presence of 47 gms. of potassium soap per liter of reaction mixture. After reaction, to 35 parts of the reaction mixture, 20 parts of 2-hydroxymethyl-1,3-dioxolane and parts 01' ethoxy ethanol were added to make a complete fluid. 7

Although, as shown in Examples 2 and 5, castor oil and blown cottonseed oil, respectively, may be caused to react with 2-hydroxy 1,3-dioxolane and thereafter the resultant product mixed with 2-hydroxy 1,3-dioxolane, it will be understood that: (1) other vegetable and animal oils, such as previosuly pointed out in detail, may also be used for this reaction; and (2) the product resulting from the oil-dioxolane reaction may be used as such, or mixed with diluents as desired. for hydraulic fluid purposes.

Various changes may be made in the details and preferred embodiments of the present invention without departing therefrom or sacrificing any of the advantages thereof.

We claim:

1. A fluid composition adapted for use in fluidactuated apparatus comprising from 5 to 95% by volume of 2-hydroxymethyl-1,3-dioxolane and from 95 to 5% of a material selected from the group consisting of animal and vegetable oils; blown animal and vegetable oils; and alcoholysis products of animal and vegetable oils and blown animal and vegetable oils.

2. A fluid. composition adapted for use in fluidactuated apparatus comprising from 5 to 95% by volume of 2-hydroxy methyl-1,3-dioxolane and from 95 to 5% of a vegetable oil.

3. A fluid composition adapted for use in fluidactuated apparatus comprising from 5 to 95% by volume of 2-hydroxy methyl-1,3-dioxolane and from 95 to 5% of castor oil.

4. A fluid composition adapted for use in fluid pressure apparatus comprising from 5 to 95% by volume of 2-hydroxy methyl-1,3-dioxolane and from 95 to 5% of a castor oil derivative of a compound containing at least 1 hydroxyl group capable of reacting with castor oil.

5. A fluid composition adapted for use in fluid pressure apparatus comprising from 5 to 95% by volume of the product obtainable by reacting a vegetable oil with 2-hydroxy methyl-1,3-dioxolane, together with from 5 to 95% by volume of 2-hydroxy methyl-1,3-dioxolane.

6. A fluid composition adapted for use in fluid pressure apparatus comprising from 5 to 95% 'by volume of the product obtainable by reacting castor oil with 2-hydroxy methyl-1,3-dioxglane, together with from 5 to 95% of Z-hydroxy methyl-1,3-dioxolane.

7. A fluid composition adapted for use in fluid pressure apparatus comprising from 5 to 95 parts by volume of 2-hydroxy methyl-1,3-dioxolane and 5 to 95 parts by volume of a product obtained by reacting castor oil with a glycol. I

8. A fluid composition adapted for use in fluid pressure apparatus comprising from 5 to 95 parts by volume of 2-hydroxy methyl-1,3-dioxolane and 5 to 95 parts by volume of a product obtained by reacting castor oil with propylene glycol.

9. A fluid composition adapted for use in fluid pressure apparatus comprising from 5 to 95 parts by ,volume of 2-hydroxy methyl-1,3-dioxolane and from 5 to 95 parts by volume of a mixture of an alcohol and the product obtained by reacting a vegetable oil with 2-hydroxy methyl-1,3-dioxolane.

10. A fluid composition adapted for use in fluid pressure apparatus comprising from 5 to 95 parts by volume of 2-hydroxy methyl-1,3-dioxolane and from 5 to 95 parts by volume of a mixture of isobutanol and the product obtained by reacting a vegetable oil with 2-hydroxy methyl-1,3- dioxolane.

11. A fluid composition adapted for use in fluid pressure apparatus comprising from 5 to 95 parts by volume of z-hydroxy methyl-1.3-dioxolane and 5 to parts by volume oi a mixture 01' isobutanol and the product obtained by reacting castor oil with a glycol.

JOHN C. WOODHOUSE. E. WALKER. 

